1. Field of the Invention
The present invention relates to an electrostatic chuck capable of clamping fixed substrates such as semiconductor wafers, metal wafers or glass substrates used in the production of semiconductor devices and liquid crystal devices, etc. using electrostatic force.
2. Background Technology
In the past, examples of apparatuses for clamping substrates such as semiconductor wafers, metal wafers or glass substrates used in the production of semiconductor devices and liquid crystal devices, etc. (to be referred to as xe2x80x9cfixed substratesxe2x80x9d) included a vacuum chuck capable of clamping fixed substrates by physically clamping the substrates using vacuum force, and a clamp capable of mechanically clamping fixed substrates.
However, in the case of using a vacuum chuck to clamp fixed substrates, due to difference in pressure between the external atmosphere and vacuum chuck under vacuum conditions, there was the problem of being unable to clamp the fixed substrates. In addition, in the case of mechanically clamping fixed substrates using a clamp, there were problems such as the locations on the fixed substrates where the clamp makes contact being unable to be used as a device, the occurrence of partial distortion in the fixed substrates, and the generation of particles caused by raising and lowering of the clamp.
Therefore, in order to solve the above problems, an electrostatic chuck is proposed that is capable of clamping fixed substrates using electrostatic force. An electrostatic chuck is mainly composed of a planar electrode and a pair of insulating members disposed in mutual opposition between which the electrode is interposed. As a result of placing a fixed substrate on one of the pair of insulating members and applying a prescribed voltage to the electrode, the fixed substrate can be clamped using electrostatic force.
In the past, compound sintered bodies, in which ceramics comprised of one type selected from titanium oxide, titanium nitride and silicon carbide were contained in ceramics such as aluminum oxide, or aluminum nitride-based sintered bodies and so forth, were proposed for the insulating members that compose such an electrostatic chuck.
However, in the case of using the above electrostatic chuck installed in an apparatus that uses plasma such as a plasma CVD apparatus, plasma etching apparatus, sputtering apparatus or ion injection apparatus, an electrical charge accumulates on the fixed substrate due to long-term plasma irradiation, and this accumulated electrical charge can cause an abnormal discharge. As a result, the electrostatic chuck may be damaged or destroyed, the fixed substrate may be damaged, or particles may be generated that have a detrimental effect on product performance.
Therefore, measures were employed in the prior art in order to prevent this abnormal discharge, examples of which include installing a ground wire on the surface of the fixed substrate to allow the electrical charge to escape, installing an electrically conductive ring around the outside of the fixed substrate to allow the electrical charge to escape, or installing an ionizer on the fixed substrate to allow the electrical charge to escape.
However, in the case of employing these measures, since it was necessary to install a ground wire, electrically conductive ring or ionizer and so forth on the fixed substrate, there was the problem of increased production costs of the electrostatic chuck.
In addition, in the case of employing the above measures, although the occurrence of abnormal discharge can be reduced, since abnormal discharge cannot be completely prevented, there was the problem of being unable to adequately prevent damage and destruction of the electrostatic chuck, damage of the fixed substrate, and the generation of particles.
The present invention was conceived to solve the above problems, and its object is to provide an electrostatic chuck that is able to completely prevent abnormal discharge that not only causes damage and destruction of the electrostatic chuck, but also causes damage of the fixed substrate as well as the generation of particles, without increasing the production cost of the electrostatic chuck.
As a result of conducting various studies to develop an electrostatic chuck having superior heat resistance and thermal shock resistance, which in addition to being able to completely prevent abnormal discharge, has at least an insulating member on the side on which the fixed substrate is placed that has low temperature dependency of electric conductivity, superior corrosion resistance to halogen gas and plasma, high strength and high hardness, the inventor of the present invention found that at least the insulating member on the side on which the fixed substrate is placed should be composed with a specific compound sintered body having for its main components silicon carbide particles and aluminum particles, thereby leading to invention of the electrostatic chuck of the present invention.
The electrostatic chuck of the present invention is an electrostatic chuck provided with a pair of insulating members disposed in mutual opposition between which an electrode is interposed, wherein a first insulating member of the above pair of insulating members at least on the side on which the fixed substrate is placed is composed of a compound sintered body having for its main components 4% by weight to 12% by weight of silicon carbide particles and aluminum particles, and the first insulating member has varistor characteristics.
The above varistor characteristics are such that the volumetric specific resistance value of the above first insulating member is from 1xc3x97109 to 1xc3x971012 xcexa9xc2x7 cm when the potential difference between the surface of the above first insulating member on which the fixed substrate is placed and the above electrode is 1000 V or less, and from 1xc3x97107 to 1xc3x97108 xcexa9xc2x7 cm when the potential difference between the surface of the above first insulating member on the side on which the fixed substrate is placed and the above electrode is 3000 V or more.
Furthermore, in the present invention, having for its main components silicon carbide particles and aluminum particles is defined as meaning that the content of silicon carbide particles and aluminum particles combined is 98% by weight or more.
The inventor of the present invention also found that by controlling the content of silicon carbide particles in the compound sintered body that composes the first insulating member on the side on which the fixed substrate is placed, the volumetric specific resistance of the first insulating member can be controlled. They also found that by making the content of silicon carbide particles in the above compound sintered body from 4% by weight to 12% by weight, the volumetric specific resistance value of the first insulating member could be made to be from 1xc3x97109 to 1xc3x971012 xcexa9xc2x7 cm when the potential difference between the surface of the first insulating member on which the fixed substrate is placed and the electrode is 1000 V or less, and from 1xc3x97107 to 1xc3x97108 xcexa9xc2x7 cm when the potential difference between the surface of the first insulating member on the side on which the fixed substrate is placed and the above electrode is 3000 V or more.
Namely, it was found that the first insulating member is provided with varistor characteristics by composing the first insulating member on the side on which the fixed substrate is placed in the manner described above, and since electrical charge accumulated on the fixed substrate can be easily discharged by providing a connecting wire and so forth to the first insulating member even in cases in which plasma is irradiated onto the electrostatic chuck for a long period of time, there is no accumulation of electrical charge on the fixed substrate, thereby making it possible to completely prevent abnormal discharge.
In addition, in the case of using the electrostatic chuck of the present invention, since electrical charge that accumulates on the fixed substrate can be easily discharged by providing a connecting wire and so forth on the first insulating member, it is not necessary to install a ground wire, electrically conductive ring or ionizer and so forth on the fixed substrate as in the prior art, thereby making it possible to reduce the production cost of the electrostatic chuck.
In addition, the inventor of the present invention found that by making the content of silicon carbide particles in the compound sintered body that composes the first insulating member from 4% by weight to 12% by weight, the hardness and strength of the first insulating member are remarkably improved, thereby reducing the generation of particles.
Moreover, the inventor of the present invention found that a first insulating member having the above composition has low temperature dependency of its electrical conductivity, superior corrosion resistance to halogen gas, superior heat resistance and thermal shock resistance, and is free of risk of damage due to thermal stress even during use at high temperatures.
In addition, the inventor of the present invention found that, in the case the average particle size of the silicon carbide particles contained in the compound sintered body that composes the first insulating member exceeds 0.5 xcexcm, the effect of improving the strength of the first insulating member due to addition of silicon carbide particles is diminished, resulting in the risk of an electrical field during plasma irradiation concentrating in the portion of silicon carbide particles and causing the area around the silicon carbide particles to be susceptible to damage.
Thus, it is preferable that the average particle size of the silicon carbide particles contained in the compound sintered body that composes at least the first insulating member of the pair of insulating members of the electrostatic chuck of the present invention be 0.5 xcexcm or less, and preferably 0.2 xcexcm or less.
In addition, the inventor of the present invention found that, in the case the average particle size of the aluminum oxide particles contained in the compound sintered body that composes the first insulating member exceeds 2 xcexcm, the first insulating member is easily etched by plasma resulting in the formation of sputtering scars on the surface of the first insulating member on the side on which the fixed substrate is placed, increased surface roughness and reduced electrostatic adsorption force of the electrostatic chuck.
Thus, it is preferable that the average particle size of the aluminum oxide particles contained in the compound sintered body that composes at least the first insulating member of the pair of insulating members of the electrostatic chuck of the present invention be 2 xcexcm or less.
In addition, the inventor of the present invention found that, in the case at least a portion of the silicon carbide particles are present within the aluminum oxide particles in the compound sintered body that composes the first insulating member, together with the plasma resistance of the first insulating member being improved, due to the gap between the silicon carbide particles becoming narrower, varistor effects can be demonstrated by adding only a small amount of silicon carbide particles.
Thus, it is preferable that at least a portion of the silicon carbide particles be formed within the aluminum oxide particles in the compound sintered body that composes at least the first insulating member of the pair of insulating members of the electrostatic chuck of the present invention.
Furthermore, a small amount of impurities are permitted in the compound sintered body that composes the first insulating member. However, in the case the fixed substrate is used in the production of semiconductor devices, the decreases in life time and gate voltage in the semiconductor device production process are caused by transition metal elements and alkaline metals. In addition, it was verified through research conducted by the inventor of the present invention that, if the amount of metal impurities other than aluminum or silicon exceeds 0.1% by weight, together with the potential for contaminating the wafer or other fixed substrate increasing, the temperature dependency of the electrical resistance of the first insulating member also becomes larger, thereby making this undesirable.
Thus, the content of metal impurities other than aluminum and silicon in the compound sintered body that composes at least the first insulating member of the pair of insulating members of the electrostatic chuck of the present invention is preferably 0.1% by weight or less.
Furthermore, although the second insulating member of the pair of insulating members in the present invention on the side on which the fixed substrate is not placed may be composed of an insulating member having a structure that differs from that of the first insulating member, it is preferable that the second insulating member also be composed of a compound sintered body having the same structure as the first insulating member.
By giving the second insulating member the same structure as the first insulating member, in addition to enabling the second insulating member to have superior corrosion resistance to halogen gas and plasma, high strength and hardness and superior heat resistance and thermal shock resistance, the production process of the electrostatic chuck can be simplified.
According to the present invention, since at least a first insulating member on the side on which a fixed substrate is placed is composed with a compound sintered body of a specific composition having satisfactory varistor characteristics, together with the occurrence of abnormal discharge in the plasma atmosphere, which causes damage and destruction of the electrostatic chuck, damage of the fixed substrate and the generation of particles, being able to be completely prevented, at least the first insulating member on the side on which the fixed substrate is placed has little temperature dependency of its electrical conductivity, superior corrosion resistance to halogen gas and plasma, high strength and hardness, and superior heat resistance and thermal shock resistance, and an electrostatic chuck can be provided that has superior response of adsorption and release of the fixed substrate.
In addition, in the case of using the electrostatic chuck of the present invention, since electrical charge that has accumulated on the fixed substrate can be easily discharged by providing a connecting wire and so forth on the first insulating member, it is no longer necessary to install a ground wire, electrically conductive ring or ionizer and so forth on the fixed substrate as in the prior art, thereby making it possible to reduce the production cost of the electrostatic chuck.